Mass Eccentricity <-- What?!

**fractalnode** · Nov27-09, 09:51 AM

Hi everyone!

Can someone define "Mass Eccentricity" for me? I looked it up in a few online dictionaries, and didn't get a definition I understood in relation to its use:

In other words, there are no injuries in static conditions without any mass eccentricities;

and

Therefore, the unique cause of all brain, spine and musculo-skeletal injuries has two components:
1. Coupled linear and angular jerks; and
2. Mass distribution with “eccentricities”.

I'm reading an interesting bio-mechanic-type paper, and got lost with this term. Hope I'm posting this is the right place. THANKS!

**wywong** · Nov27-09, 08:09 PM

I guess it means off-centered mass distribution.

During impact, if the impact force is lopsided, some parts of the body will experience shear stress and bending stress that can more easily cause injury than compression stress.

If the impact force is evenly distributed (e.g. exerted by a fluid like inside the cranial cavity), the damage should be minimal. However, if the mass distribution is unbalanced the off-centered inertial force will still cause shear and bending stress and result in injury.

I may be wrong, but I doubt the paper's argument because all body parts, including the brain and body fluids, have density about that of water, so there won't be much mass eccentricity.

Wai Wong

**fractalnode** · Nov27-09, 08:28 PM

Cool, Thank You!

This makes sense. The paper is referring almost specifically to injuries involving two components. Like a car crash, or a person's leg receiving an impact while their weight is placed on it. I don't think the paper is accounting for extreme forces, but it is interesting nonetheless.

If anyone wants the link, here it is.